1. Field of the Invention
The present invention relates to a device for sensing the opening degree of a valve, and more particularly to a device for sensing the opening degree of a valve, which can easily determine the upper and lower limits without using upper and lower limit switches so that, besides simplifying the mechanical structure, the device can be easily installed, maintained, and repaired.
2. Description of the Prior Art
As generally known in the art, a valve opening degree sensing device is connected to a valve, which adjusts the flow of a fluid (e.g. air, water, oil), and senses the movement of the valve. The user checks the operating condition of the valve measured by the valve opening degree sensing device, and adjusts the flow of the fluid by controlling the operation of the valve at a desired level. The application of a valve and a valve opening degree sensing device ranges from large facilities (e.g. oil pipelines) to small devices (e.g. mixed air supply devices of automobiles and motorcycles).
A conventional valve device has a valve installed inside a pipe-shaped tube, through which a fluid is transferred, and the transfer of the fluid is controlled by opening/closing the valve. To this end, the valve is connected to a valve driving device via a shaft, which extends through the pipe to connect the valve and the driving device. The driving device or the shaft is connected to an opening degree sensing device, which senses the degree of opening based on the movement of the driving device or the rotation of the shaft. The driving device and the opening degree sensing device are connected to a control panel, which adjusts the opening/closing of the valve by remote control or by the user.
FIG. 1 shows the brief construction of a conventional valve, a valve driving device, and an opening degree sensing device.
Referring to FIG. 1, a valve 3 is installed inside a pipe 1, through which a fluid is transferred, to adjust the amount of transferred fluid. The valve 3 is driven by a shaft 5, which is coupled to the valve 3 through the pipe 1. To this end, the shaft 5 is mechanically coupled to the driving device 10. The driving device 10 includes an actuator 7 (or motor) for providing the shaft 5 with physical driving force, and a controller 9 for controlling the actuator 7. An opening degree sensing device 11 is installed on an end of the shaft 5 to detect the degree of rotation of the shaft 5 and display it. To this end, the opening degree sensing device 11 includes a sensor 13 and a beacon 15 for displaying the degree of opening.
FIG. 2 is a top view briefly showing the interior of the opening degree sensing device, and FIG. 3 is a lateral view briefly showing the interior of the opening degree sensing device.
Referring to FIGS. 2 and 3, the conventional opening degree sensing device 13 includes a main gear 17, cams 19 (19a and 19b), upper and lower limit switches 21 (21a and 21b), and a potentiometer 25. The main gear 17 is coupled around the shaft 5. A meter gear 23, which has a predetermined gear ratio with regard to the main gear 17, is installed and positioned to engage with the main gear 17 so that rotation of the shaft 5 is transferred to the meter gear 23 via the main gear 17. The meter gear 23 is connected to the potentiometer 25 by a meter shaft 27 to transmit rotation of the main gear 17 to the potentiometer 25. The potentiometer 25 generally consists of a variable resistor, which changes the voltage or current as the meter gear 23 rotates and which displays the change (i.e. degree of opening) to the outside.
The valve 3 shown in FIG. 1 is rotated about 90° inside the pipe 1 to adjust the flow rate. As a result, the main gear 17 rotates about a quarter turn in the forward or backward direction, and the meter gear 23 rotates by a predetermined amount. The valve 3 switches between a closed condition, in which it blocks the pipe 1 and allows no fluid movement, and a fully open condition, in which the valve 3 is fully open and maximizes the fluid movement. In order to efficiently adjust and sense the closed and fully open conditions, the opening degree sensing device 13 is provided with means for controlling or sensing the open/closed condition of the valve when it is in the closed condition (i.e. when the rotational angle is about 0°) and when it is in the fully open condition (i.e. when the rotational angle is about 90°). Particularly, upper and lower limit switches 21 and cams 19 are used to recognize the closed and fully open conditions, as shown in FIGS. 2 and 3. The upper and lower limit switches 21 include an upper limit switch 21a and a lower limit switch 21b. Respective switches 21 match with a pair of cams 19 coupled to the shaft 5. The cams 19 installed on the shaft 5 are installed to contact different switches 21 when the valve angle is about 0° and 90°, respectively. Particularly, the second cam 19b presses the switch lead 22 of the lower limit switch 21b when the valve angle is about 90°, and the first cam 19a presses the switch lead 22 of the upper limit switch 21a when the valve angle is about 0°. When the switch leads 22 of the upper and lower limit switches 21 are pressed by the cams 19 in this manner, the driving device 11 stops driving the valve 3 to prevent excessive rotation of the valve 3. This prevents the valve from being damaged, and controls the flow rate at the maximum or minimum level. To this end, a toothed spline 29 is formed on the shaft 5 to couple the cams 19 to the shaft 5 in a reliable and easy manner.
However, the conventional opening degree sensing device has a problem in that its installation, maintenance, and repair are difficult, the upper and lower limits must be determined manually, the error ratio is high, and the output type is limited. More particularly, use of mechanical upper and lower limit switches requires that the valve must be correctly positioned before installing the cams. In the case of incorrect installation, the measurement range is reduced, or a partially open condition is frequently mistaken for a closed condition, which makes the fluid control difficult.
The mechanical upper and lower limit switches, cams, and spline are worn down by long-period driving, and their maintenance and repair degrade user convenience. Furthermore, there is no general method for compensating for the clearance of each existing device. In other words, the clearance must be corrected manually by the user. There are even a number of components, including the spline 29 and cams 19, the clearance of which is not easily reduced. This makes it difficult to improve measurement precision. In addition, there is no method for sensing the degree of opening based on consideration that the clearance increases as the valve 3, driving device 10, and sensing device 11 are used for a long period of time while undergo mechanical wear. Therefore, it is necessary to develop an opening degree sensing device which solves the above-mentioned problems and which guarantees convenient use and correct sensing.